MESSENGER mission to Mercury

[Rick]

MESSENGER Executes Last Orbit-Correction Maneuver, Prepares for Impact

MESSENGER mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., conducted the last of six planned maneuvers on April 24 to raise the spacecraft's minimum altitude sufficiently to extend orbital operations and further delay the probe's inevitable impact onto Mercury's surface.

With the usable on-board fuel consumed, this maneuver expelled gaseous helium -- originally carried to pressurize the fuel, but re-purposed as a propellant. Without a means of boosting the spacecraft's altitude, the tug of the Sun's gravity will draw the craft in to impact the planet on April 30, at about 8,750 miles per hour (3.91 kilometers per second), creating a crater as wide as 52 feet (16 meters).

The previous maneuver, completed on April 14, raised MESSENGER's minimum altitude above Mercury from 6.5 kilometers (4.0 miles) to 13.3 kilometers (8.3 miles). But because of progressive changes in the orbit over time, the spacecraft's minimum altitude continued to decrease.

At the start of yesterday's maneuver, at 1:23 p.m. EDT, MESSENGER was in an orbit with a closest approach of 8.3 kilometers (5.1 miles) above the surface of Mercury. With a velocity change of 1.53 meters per second (3.43 miles per hour), the spacecraft's four largest monopropellant thrusters released gaseous helium to nudge the spacecraft to an orbit with a closest approach altitude of 18.2 kilometers (11.3miles).

Mission controllers at APL verified the start of the maneuver 9.4 minutes later, when the first signals indicating spacecraft thruster activity reached NASA's Deep Space Network (DSN) tracking station in Goldstone, California. This was the third MESSENGER maneuver designed to adjust the course of the spacecraft using just helium gas.

More: http://messenger.jhuapl.edu/news_room/details.php?id=282

[ApophisAstros]

The first to orbit Mercury, the MESSENGER spacecraft came to rest on this region of Mercury's surface yesterday. Constructed from MESSENGER image and laser altimeter data.......

http://apod.nasa.gov/apod/ap150501.html

roger

[Rick]

NASA Completes MESSENGER Mission with Expected Impact on Mercury's Surface

Mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., confirmed today that NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft impacted the surface of Mercury, as predicted, at 3:26 p.m. EDT this afternoon (3:34 p.m. ground time).

Mission controllers were able to confirm the end of operations just a few minutes later at 3:40 p.m., when no signal was detected by the Deep Space Network (DSN) station in Goldstone, California, at the time the spacecraft would have emerged from behind the planet had MESSENGER not impacted the surface. This conclusion was independently confirmed by the DSN's Radio Science team, who were simultaneously looking for the signal from MESSENGER from their posts in California.

MESSENGER was launched on August 3, 2004, and it began orbiting Mercury on March 18, 2011. The spacecraft completed its primary science objectives by March 2012. Because MESSENGER's initial discoveries raised important new questions and the payload remained healthy, the mission was extended twice, allowing the spacecraft to make observations from extraordinarily low altitudes and capture images and information about the planet in unprecedented detail.

Last month -- during a final short extension of the mission referred to as XM2'-- the team embarked on a hover campaign that allowed the spacecraft at its closest approach to operate within a narrow band of altitudes, 5 to 35 kilometers above the planet's surface. On April 28, the team successfully executed the last of seven orbit-correction maneuvers (the last four of which were conducted entirely with helium pressurant after the remaining liquid hydrazine had been depleted), which kept MESSENGER aloft for the additional month, sufficiently long for the spacecraft's instruments to collect critical information that could shed light on Mercury's crustal magnetic anomalies and ice-filled polar craters, among other features.

With no way to increase its altitude, MESSENGER was finally unable to resist the perturbations to its orbit by the Sun's gravitational pull, and it slammed into Mercury's surface at around 8,750 miles per hour, creating a new crater up to 52 feet wide.

More: http://messenger.jhuapl.edu/news_room/details.php?id=284

[Rick]

MESSENGER Finds Evidence of Ancient Magnetic Field on Mercury

Mercury's magnetic field, generated by a dynamo process in its outer core, has been in place far longer than previously known, a paper by MESSENGER Participating Scientist Catherine Johnson reports.

About 4 billion years ago, Mercury's magnetic field could have been much stronger than today, as indicated by low-altitude observations made by NASA's MESSENGER spacecraft that revealed evidence of magnetization of ancient crustal rocks on Mercury.

The MESSENGER spacecraft crashed onto Mercury last week after running out of fuel, but the mission provided a trove of new information on the planet closest to the Sun.

More: http://messenger.jhuapl.edu/news_room/details.php?id=285

[Rick]

Mercury Gets a Meteoroid Shower from Comet Encke

The planet Mercury is being pelted regularly by bits of dust from an ancient comet, a new study has concluded. This has a discernible effect in the planet's tenuous atmosphere and may lead to a new paradigm on how these airless bodies maintain their ethereal envelopes.

The findings are to be presented at the annual Meeting of the Division of Planetary Sciences of the American Astronomical Society at National Harbor, Maryland, this week, by Apostolos Christou at the Armagh Observatory in Northern Ireland, Rosemary Killen at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and Matthew Burger of Morgan State University in Baltimore, working at Goddard.

Earthlings are no strangers to the effects of cometary dust on a planet and its environment. On a clear, moonless night we witness the demise of countless such dust grains as they burn up in the Earth's atmosphere in the form of meteors or "shooting stars." At certain times of the year, their numbers increase manyfold, creating a natural fireworks display: a meteor shower. This is caused by the Earth passing through a stream of dust particles left behind by certain comets.

More: http://www.nasa.gov/feature/goddard/mercury-gets-meteoroid-shower-from-comet-encke

[Rick]

MESSENGER Data May Reveal the Remains of Mercury's Oldest Crust

Mercury's surface is unusually dark, an observation that until recently had planetary scientists mystified. But in a new study published March 7 2016 in Nature Geoscience, a team of researchers provides evidence that the darkening agent is carbon, a finding that offers important clues to the nature of the planet's original crust.

Patrick Peplowski, a research scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, and lead author of the paper, explains that earlier measurements of the chemistry of Mercury's surface only added to this mystery because they indicated that Mercury's surface has low abundances of iron and titanium, important constituents of the most common darkening agents on the Moon and other silicate bodies.

"A process of elimination led prior researchers to suggest that carbon may be the unidentified darkening agent, but we lacked proof," he said. "Spectral modeling of MESSENGER color imaging data suggested that weight-percent levels of carbon, likely in the form of graphite, would be required to darken Mercury's surface sufficiently. This level is unusually high, given that carbon is found at typical concentrations of only ~100 parts per million on the Moon, Earth and Mars."


More: http://messenger.jhuapl.edu/news_room/details.php?id=291

[Rick]

Researchers Trace Mercury's Origins to Rare Enstatite Chondrite Meteorite

Around 4.6 billion years ago, the universe was a chaos of collapsing gas and spinning debris. Small particles of gas and dust clumped together into larger and more massive meteoroids that in turn smashed together to form planets. Scientists believe that shortly after their formation, these planets — and particularly Mercury — were fiery spheres of molten material, which cooled over millions of years.

Now, geologists at MIT have traced part of Mercury's cooling history and found that between 4.2 and 3.7 billion years ago, soon after the planet formed, its interior temperatures plummeted by 240 degrees Celsius, or 464 degrees Fahrenheit.

They also determined, based on this rapid cooling rate and the composition of lava deposits on Mercury's surface, that the planet likely has the composition of an enstatite chondrite — a type of meteorite that is extremely rare here on Earth.

More: http://news.mit.edu/2016/mercury-origins-rare-meteorite-0627